One of the causes that produce tire noise is cavity resonance sound arising from vibration of air charged into the cavity of a pneumatic tire. When the tire is run on a road surface under load, the tread portion of the tire that contacts it vibrates because of the irregularity of the road surface, and the vibration of the tread portion causes the air within the tire cavity to vibrate, thereby producing the cavity resonance sound. It is known that the frequency of sound heard as noise in the cavity resonance sound is near 250 Hz.
As an approach for reducing such cavity resonance sound, the present applicants have proposed a pneumatic tire which can effectively reduce the cavity resonance sound, the tire having porous members of resin foam such as urethane foam placed within the tire cavity in such a manner that the cross-sectional area of the tire cavity varies around its circumference (for example, see Patent Document 1). The porous members, which are in the form of rectangular solids, are mounted on the inner surface of the tread portion of the pneumatic tire along therewith with an elastic fixing band.
However, with respect to the porous members mounted on the inner surface of the tire as described above, it has found in actual vehicle running tests that the corners located on the opposite sides, in the widthwise direction of the porous member, of the ends positioned back and forth in the rotation direction of the tire, especially the back end, drop out and are damaged early; there is still room for improvement in terms of durability. Patent Document 1: Japanese Patent Application Kokai Publication No. 2002-28432